back from the dead, fun leftovers to be used !

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ben_mtl
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back from the dead, fun leftovers to be used !

Post by ben_mtl » Mon Oct 29, 2018 7:30 am

Hello everyone,
It's been a while since I've been here.. and even more time since I built my last pair of planks..
After I built my first pair, 10 years ago, I was taking small orders for friends and such because I liked it... the materials paid for themselves I was was paid by having fun doing it.. but without noticing, I wasn't building for me anymore.. and slowly lacked the fun part of building.
3 years ago I took my last "order". It was a mistake, I was not in a good shape to do that... I was just back from a brain surgery, had memory problems from that... basically I wasn't as "sharp" as I used to be... I felt pushed to complete the order "on time", and it was definitely the toughest one of my ski-building career because I used materials I never used before (basla cores, and flax fiber from bComp).. That was the last time I built skis... I had a couple cores (regular maple/poplar) ready for me but they have been sitting in the garage for 3 years, no motivation at all !

.. until now !
I feel the pleasure of working in my shop, and the plan is to complete the 2 pairs that have been sitting around, and also build a 3rd pair with leftovers from the last order (balsa cores) and some samples that also have been taking dust for quite some time now (triax carbon !), and I also have some 6K 0/90degree braided carbon if needed ... (I don't know why I bought this one in the first place... maybe another project I forgot about...)
The goal is to build a super-light touring/powder ski.. not because my regular skis are particularly heavy (they're not), but just because I can !

But, I feel like I'm starting from scratch like 10 years ago for the balsa/carbon ski.. I've read a few topics here with lots of good info but I'd like to present my project so maybe I can have some more input on what I'm planning. I only have material for 1 attempt, I'd like not to f**k it up too much. Here's the plan, and the things I'm thinking about :

- Regular Durasurf 4001 base
- regular edges + VBS
- Blasa core from bComp, with maple sidewalls, poplar bindings reinforcements (where I'll put inserts), and UHMW tispacers as usual.
- Triax carbon (8 Oz fabric from "braider.com", 0°/+60°/-60°) top and bottom
- Printed nylon topsheet OR clear Duravision5050 with white screenprinted design (if I find the motivation to get into screenprinting again...)

So, first thing that hit my mind is the amount of carbon to use to kinda match my actual typical layup (22Oz Triax + 3in 4 Oz UD carbon strip, top and bottom).
The fabric used is not the only factor to consider, I know that, usually when you switch to carbon (of equivalent strength) you have to make you core a bit thinner. However I plan on keeping the same core thickness since I'm switching from a stiff poplar/maple combo to balsa which is kinda soft/souple.
Then, since I've read carbon can be considered 3 time stronger than fiberglass for the same weight.. 1 layer of 8 Oz triax carbon should get me pretty close to my 22 Oz fiberglass.. but do I need more ? Should I also add the 3in UD strip to keep the skis "pop" ? Anyone has something to suggest ?

That's it for now ! thanks for reading :)
A bad day skiing is always better than a good one at work...

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vinman
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Post by vinman » Mon Oct 29, 2018 4:53 pm

Welcome back! I think the 8 oz carbon plus a balsa core sounds interesting. It think it is tough to gauge core thickness with this for me at least. I'd go with not 1 layer of carbon. Id also error on th side of a soft ski, too stiff is worse than too soft I think.
Fighting gravity on a daily basis
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chrismp
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Post by chrismp » Tue Oct 30, 2018 12:18 am

We typically use 13 oz/yd triax carbon (+/-45 and 0) with equal distribution of fabric weight on each axis in combination with harder core woods.

Bcomp can help you with the right core thickness. If you tell them what types of wood and reinforcement fabrics you have used in the past, they will calculate the required core thickness to get an equally stiff ski.

Here's a link to their form for this type of request: http://bcomp.ch/media/profile_calculati ... i_2017.pdf

ben_mtl
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Post by ben_mtl » Tue Oct 30, 2018 7:26 am

thanks for the link, I just sent a message to Bcomp with all the data I have regarding my actual process VS the "new" materials I have on hand and am planning on using... will see what they suggest.

Usually you try to switch one material at a time to tweak you process and keep consistant results.. this time almost everything is changed at once !
I'm trying to get the best "pre-build info" to get things working.. but in the end even if I get a complete piece of crap it won't be worse than having materials sleeping forever in the garage.. at least it might look cool nailed on the wall !
A bad day skiing is always better than a good one at work...

rswilliams13
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Post by rswilliams13 » Thu Nov 01, 2018 10:57 am

One thing to keep in mind when using carbon that most people don't realize is that carbon is not much stronger by weight than glass if at all. It's almost 3 times stiffer, but not much stronger and fails with much less elongation. I made a few snowboards with a light all carbon layup and had the first composite failures I've ever had. The boards snapped pretty easily. Jones snowboards is making some full carbon designs, and they are having a ton of failures. If you want a strong ski, use close to the same weight of carbon as you would glass, and thin out the core to get the desired flex. The reduced core thickness is where a large part of the weight savings should come from. Also carbon transfers vibration really well. I'd consider using one layer of your carbon with some biaxial glass. I've settled on a carbon/glass hybrid layup, and lose about 25% fabric weight and some additional weight from the thinner core without sacrificing strength. That's my $.02

ben_mtl
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Post by ben_mtl » Fri Nov 02, 2018 4:22 am

rswilliams13 wrote:One thing to keep in mind when using carbon that most people don't realize is that carbon is not much stronger by weight than glass if at all. It's almost 3 times stiffer, but not much stronger and fails with much less elongation. I made a few snowboards with a light all carbon layup and had the first composite failures I've ever had. The boards snapped pretty easily. Jones snowboards is making some full carbon designs, and they are having a ton of failures. If you want a strong ski, use close to the same weight of carbon as you would glass, and thin out the core to get the desired flex. The reduced core thickness is where a large part of the weight savings should come from. Also carbon transfers vibration really well. I'd consider using one layer of your carbon with some biaxial glass. I've settled on a carbon/glass hybrid layup, and lose about 25% fabric weight and some additional weight from the thinner core without sacrificing strength. That's my $.02
That's very interesting . It's good idea to add some fiberglass biax.. but I don't have that on hand and the idea is to use mainly leftovers. The only fiberglass I have is my 22Oz triax... I'll look into that though !

Just got some news from Braider (carbon triax supplier), What the engineer there says is that basically their carbon fiber is 4 to 5 times stiffer than fiberglass for the same weight.

Starting from there,
My triax is 22 Oz split like so : 10.2Oz@0°/ 5.6Oz@+45° / 5.6Oz@-45°
On the other hand, their Qiso Light is 8Oz total, split equally in every direction -» 2.7Oz@0° / 2.7Oz@+60° 2.7Oz@-60°

In theory I'm pretty close at 0° if we consider carbon = 4x fiberglass, and for the other directions carbon will make it slightly stiffer "torsionnaly".
However, the engineer at Braider suggests I also use the carbon biax fabric I have (6K, 2x2 twill) in addition to their Qiso... I did the math and overall this would make a ski 3x stiffer that with my regular fiberglass triax layup. With a total fabric weight of +-18Oz.

Now, I'm planning on using a balsa core (Bcomp) instead of my regular maple/poplar/ash combo. Balsa is ways softer, usually just switching from traditional woodcore to balsa core (keeping everything else as is) you have to significantly increase your core thickness. I'm still waiting for some info from Bcomp that might (or might not) crush my dream, but I feel quite confident I can achieve a ski similar to my usual layer using both the carbon fabrics I have + balsa core with minimal change to my core dimensions (might even have to make it thinner !)

Will keep you posted !
A bad day skiing is always better than a good one at work...

sammer
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Post by sammer » Fri Dec 14, 2018 6:23 pm

Welcome back Ben!!!

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)

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